1. Field of the Invention
This invention relates to a method for precision casting of titanium or titanium alloy applicable for obtaining precision castings of titanium or titanium alloy which are excellent in heat-resisting property and corrosion resistance in addition to their lightness, and which have very high strength.
2. Description of the Prior Art
Titanium and titanium alloy are light and excellent in heat and corrosion resistance and in mechanical strength. Therefore it is expected that useful products can be obtained by the precision casting of titanium or titanium alloy.
However, because the titanium or titanium alloy has a melting point higher than 1400.degree. C. and is also active, there is a problem in that there are great difficulties in melting and casting the titanium or titanium alloy in the majority of cases.
Namely, when an ordinary ceramic crucible is used in order to melt the titanium or titanium alloy and obtain the quantity and temperature of the molten metal suitable for the casting, there is a problem in that oxide ceramics forming the crucible can be easily reduced by titanium at a high temperature. If a graphite crucible is used, there is another problem in that it is only possible to carry out the melting in a small quantity for a short time from a standpoint of preventing the titanium or titanium alloy from contamination because carbon dissolves into the titanium or titanium alloy. In regard to a mold for casting the molten metal of the titanium or titanium alloy thereinto, a reaction sometimes takes place between the mold and the molten metal. In this case, it is necessary to reduce the casting temperature as much as possible, however the molten metal is apt to solidify before the mold cavity is filled sufficiently with the molten metal in such a case and there is a different problem in that a misrun of the molten metal is caused in precision castings having thin-walled and complicated shapes.